Mountain Bike purchasing advice

Question
Scottgem, I have been looking into purchasing a new mountain bike for a while now.  My problem is that there are so many models to choose from, I don't know how to narrow it down myself.  My main concerns are durabilty and cost.  I'd prefer to spend less than 500, at most 600.  My last bike was a Schwinn Aluminum Comp sold at Wal-mart.  It held up ok untill I started riding more aggresively on trails.  Then I started having problems with bent rims, broken derailers, etc.  So I need a tough bike.  I have been recommend the Trek 4500, Gary Fisher Marlin.  Do you think these bikes will serve my purpose?  Do you have any other bikes in mind that are in the same class or one class higher (not over $600).
Thanks
-Nathan

Answer
Mountain bikes are not my strong suit. But another brand to look at is Iron Horse. I have an Iron Horse road bike and we recently had a rep from their company speak at our bike club. I was impressed with their offerings in the mountain bike line. Your price range should get you a decent bike no matter what you buy.

Hope this helps,
Scott<>